Conventionally, there is proposed a technique of a head-up display letting a driver see an image indicating information on the driving of the vehicle from the eye position (eye point) as a virtual image. Patent Reference-1 discloses an information display device capable of being installed in a vehicle to function as a head-up display. It also functions as a portable information display device when it is detached from the vehicle. The information display device according to Patent Reference-1 inverses the image for displaying on the display screen when detecting that it is used as a head-up display.
Patent Reference-1: Japanese Patent Application Laid-open under No. 2001-333351